Urine specimen collection methods ranges from non-invasive to invasive. The required selection method is determined by the purpose of the test and the clinical situation.
Common Methods of Urine Specimen Collection
1. Routine Void Urine Specimen Collection
A routine void specimen needs no planning and is obtained by making the patient urinate into a suitable non-sterile container. In this manner, random and early-morning specimens are collected.
2. Midstream and Clean-Catch Urine Specimen Collection
A clean-catch or midstream specimen is collected if a culture and susceptibility testing is required, or if the specimen is likely to be infected by vaginal discharge or bleeding. To ensure a clean-catch urine specimen, the urinary meatus must be meticulously cleaned with an antiseptic preparation to avoid contamination by foreign microorganisms. The foreskin is retracted and the meatus is cleansed in male patients. The cleaning agent must then be carefully removed or wash off because it can inhibit the growth of any bacteria in the specimen affecting the culture and susceptibility testing. A midstream urine collection occurs when a patient starts to urinate into a bedpan, urinal, or toilet and then stops. This flushes the urine from the distal urethra. The patient voids 3 to 4 ounces of urine into a sterile container, which is then capped, and the patient is able to finish voiding.
3. 24-Hour Urine Collection
The patient is told to urinate and discard the first specimen (eg, at 8:00 am on day 1). This is the moment that the 24-hour set begins. The patient gathers all urine voided up to and including 8:00 a.m. the next morning (day 2). The total volume of the sample is recorded in the laboratory. After thoroughly mixing the specimen, a measured sample is taken for examination.
If any urine is withheld or discarded during a timed collection, the entire timed collection is rendered invalid. Urine specimens collected over a 24-hour period are more reliable than specimens collected over a shorter period. Some analytes are excreted at different rates during the day or night, and random specimens can skip the time of maximum excretion. Furthermore, since higher concentrations of an analyte are present in a 24-hour collection, the possibility of a false-negative result is decreased. A 24-Hour Urine Collection can be easily collected using the following guidelines;
- Start the 24-hour collection by throwing away the first urine specimen.
- Collect all urine that has been voided in the next 24 hours.
- Show the patient where to keep the urine.
- During the collection period, keep the urine on ice or refrigerated. Foley bags are kept in an ice basin. Some collections necessitate the use of a preservative. Consult the laboratory.
- To avoid accidentally discarding a specimen, post the hours for urine collection in a prominent location.
- Instruct the patient to urinate before defecating to avoid contaminating the urine with stool.
- Remind the patient not to dispose of toilet paper in the urine collection container.
- Collect the final specimen as close to the end of the 24-hour cycle as possible. Include this urine in the sample.
Special Urine Collection Methods
When the more traditional collection methods fail to yield a specimen, special collection methods are indicated.
4. Urethral Catheterization
A urine specimen may be collected by inserting a sterile catheter into the bladder via the urethra. While catheterization can cause infection, it is used when patients are unable to urinate or cannot urinate when the specimen is needed (eg, during trauma).
In patients who have an indwelling urinary catheter, a specimen is collected by applying a syringe to the catheter at a point distal to the sleeve leading to the balloon. Many tubes have an entry (sampling port) area for this form of collection technique. Urine is aspirated and stored in a sterile urine bottle. (Typically, the catheter tubing distal to the puncture site must be clamped for 15 to 30 minutes prior to aspiration of urine to allow urine to ill the tubing. The clamp is removed after the specimen has been withdrawn.) The urine that accumulates in a plastic reservoir bag should never be used for a urine test.
5. Suprapubic Aspiration
In suprapubic aspiration, urine is obtained directly from the bladder by inserting a needle through the abdominal wall and into the bladder. The urine is aspirated into a syringe and sent for examination. This approach is primarily used to collect urine for anaerobic culture, when specimen contamination is inevitable, and in infants and young children. Complications are extremely rare.
6. Pediatric Collections
A pediatric collection bag is often used to obtain urine specimens from babies and young children. A hypoallergenic skin-adhesive backing surrounds the opening of this clear, pliable polyethylene pocket. Before applying the specimen bag to the skin, the perineal skin is cleansed and dried. In male children, the bag is placed over the penis, while in female children, the bag is placed over the vagina (excluding the rectum). The patient is monitored every 15 minutes after the bag is placed before the urine is collected. As soon as the urine is collected, the specimen bag should be removed. For transportation, bags can be folded and self-sealed. A tube is attached to the bag and connected to a storage container if a 24-hour specimen is needed. This eliminates the need for repeated skin preparation and adhesive reapplication to the child’s sensitive skin.